Bash Cheat Sheet

File Management

Creates a temporary file with a random name. Guarantees that the new file doesn’t exist:

mktemp

Creates both new_file.txt and new_file_2.txt:

touch new_file.txt new_file_2.txt
touch {new_file, new_file_2}.txt

Creates file_name_a, file_name_b, and file_name_c:

touch file_name_{a..c}

Creates file_name_1, file_name_2, and file_name_3:

touch file_name_{1..3}

Copies file:

cp file_name.txt file_name_copy.txt

Moves/renames file:

mv file_name.txt new_file_copy.txt

Print file contents:

cat file_name.txt

Print first 10 lines:

head file_name.txt

Print last 10 lines:

tail file_name.txt

Remove file:

rm file_name.txt
rm -f file_name.txt   # ignore if missing

Compression and Decompression

Archive files:

zip archive_name.zip file1 file2
tar -cvf archive_name.tar file1 file2
tar -zcf archive_name.tar.gz file1 file2

Archive directory:

zip -r archive_name.zip directory
tar -cvf archive_name.tar directory
tar -zcf archive_name.tar.gz directory

Extract archive:

unzip archive_name.zip
tar -xvf archive_name.tar
tar -zxvf archive_name.tar.gz

Replacing in Files

Replace text in place:

sed -i 's/search/replace/' file.txt

Replace globally and save to new file:

sed 's/search/replace/g' file.txt > new_file.txt

Search in Files

Search for text:

grep 'pattern' file.txt

Recursive search:

grep 'pattern' directory -r

Case insensitive:

grep -i 'pattern' directory

Show line numbers:

grep -n 'pattern' directory

Show matching filenames only:

grep -l 'pattern' directory

Invert match:

grep -v 'pattern' directory

Directories

Navigate:

cd directory
cd -   # previous dir
cd ~   # home dir
cd ..  # up one level

List contents:

ls
ls -a   # include hidden
ls -l   # long format
ls -lh  # human readable
ls -t   # sort by modification time

Show tree:

tree
tree -d   # directories only
tree -a   # include hidden

Create directories:

mkdir new_dir
mkdir -p parent/child/nested

Move/copy directories:

mv old_dir new_dir
cp -r directory directory_copy

Remove directories:

rmdir directory
rm -r directory

Symbolic Links

Create symlink:

ln -s path link

Overwrite symlink:

ln -sf path link

Permissions

Octal to symbolic mapping:

0 --- none
1 --x execute
2 -w- write
3 -wx write+exec
4 r-- read
5 r-x read+exec
6 rw- read+write
7 rwx full

Examples:

chmod 777 file    # all perms (insecure)
chmod 755 file    # owner rwx, others r-x
chmod 644 file    # owner rw, others r

Change ownership:

chown user file
chown :group file
chown user:group file

Arrays

Indexed array:

arr=(one two three)

Associative array:

declare -A assoc=([key1]=val1 [key2]=val2)

Add element:

arr+=(new)
assoc+=( [key3]=val3 )

Print:

echo ${arr[@]}
echo ${!assoc[@]}   # keys
echo ${assoc[@]}   # values

Delete element:

unset arr[2]
unset assoc[key1]

Resource Usage and Processes

Show processes:

top
ps all
pidof name

Change priority:

nice -n 10 process
renice 10 pid

Kill process:

kill pid
killall name

Jobs/background:

jobs
jobs -p

System usage:

free      # memory
du        # directory sizes
df        # disk usage
lsof      # open files

Shutdown and Reboot

shutdown        # 1 min\shutdown now    # immediate
shutdown +10    # 10 min
shutdown -r     # reboot
shutdown -c     # cancel
reboot          # reboot
reboot -f       # force reboot

Scheduled Tasks (cron)

Format: minute hour day month weekday command

Minute: 0–59
Hour: 0–23
Day: 1–31
Month: 1–12
Weekday: 0–6 (Sun=0 or 7)

Examples:

* * * * * cmd        # every minute
@daily cmd           # daily
@monthly cmd         # monthly
@reboot cmd          # on reboot
0 12,15,17 * * * cmd # specific hours

Edit/view/remove crontab:

crontab -e
crontab -l
crontab -r

Tmux Basics

tmux               # start
<prefix> + %       # split horizontal
<prefix> + "       # split vertical
<prefix> + arrow   # move panes
<prefix> + c       # new window
<prefix> + n       # next window
<prefix> + p       # previous window
<prefix> + d       # detach

HTTP Requests

curl https://example.com
curl -i https://example.com   # include headers
curl -o file.txt https://example.com
curl -H "User-Agent: X" https://example.com

Network and DNS

ip addr              # show IPs
ip route show        # routes
ping host            # ping
ping -c 15 -i 3 host # 15 pings every 3s

netstat -l   # open ports
netstat -i   # interface stats
traceroute host

nmap 0.0.0.0             # common ports
nmap 0.0.0.0 -p1-65535   # all ports

host example.net         # DNS lookup
dig example.net          # full DNS
dig example.net +short   # short

SSH

ssh hostname                # default user, port 22
ssh user@host               # with username
ssh user@host -p 2222       # custom port